Inflorescence morphology, heterochrony, and phytogeny in the mimosoid tribes ingeae and acacieae (Leguminosae: Mimosoideae)

Abstract

In earlier work (Grimes, 1992) on inflorescence morphology in the mimosoid tribes Ingeae and Acacieae I proposed that differences in inflorescence morphology result from three properties: the organization of components of the inflorescence and their relative positions; the hierarchical arrangement of the axes of the inflorescence and the position they assume in total tree architecture; and the heterochronic development of components of the inflorescence. Further work shows that the first two properties are better stated in terms of heterochrony; namely, that the organization of components of the inflorescence differs due to differences in timing of the development of organ systems and that the hierarchy of axes likewise differs due to heterochronic changes. Neither de novo origin of organs or organ systems nor suppression or loss of organs or organ systems accounts for the diversity in form. Observed heterochronic differences in the inflorescence structure may be divided into three types: spatial differences in the relationship between the unit inflorescence and the subtending leaf (hysteranthy); differences in the time of formation and/or the duration of whole axes; and changes in development pathways, leading to shoot dimorphism. These heterochronies are used as characters in a cladistic analysis, and it is shown that although some are homoplasious, many provide synapomorphies of clades of exemplars representing genera in the Ingeae and Acacieae.